Generally, solid-state lighting is of growing interest for residential, automotive and professional applications. Since solid-state lamps, such as LEDs, cannot be supplied from a battery or the AC mains directly, electronic power drivers (also called power supply devices) are needed for power effective driving. For efficiency reasons, LED drivers have to be operated in a switched mode. The drivers convert the available DC or AC voltage into a DC current supplied to the LEDs. The electronic driver has to provide a DC output current which is independent of variations of the input voltage source and of voltage drops at the LEDs. In most applications galvanic isolation is another important requirement for LED drivers.
Power supplies for supplying LEDs and other loads, are for example known from US 2005/0225176 A1, US 2003/0067791 A1, US 2006/0077600 A1 or WO 2005/036726.
Generally, switched mode power supplies generate a DC output voltage, wherein in most cases the output voltage is controlled by pulse width modulation (PWM). To use this driver concept within LED lighting systems, a current controller unit including a current sensor has to be added. For galvanic isolating driver circuits, the current has to be measured on the secondary side while the PWM control and the transistors are located on the primary side. This causes additional effort since an auxiliary voltage is needed on the secondary side and galvanic isolation has to be foreseen in the feed back path. If the current measurement is based on a cheap and simple shunt resistor additional losses occur.
Another problem of this known concept can be seen in EMI (electromagnetic interference) distortion typically related to PWM switching topologies.